CCN Lecture 6(1)
-
Upload
muhammad-ali -
Category
Documents
-
view
219 -
download
0
Transcript of CCN Lecture 6(1)
-
8/3/2019 CCN Lecture 6(1)
1/33
1
Introduction
Many times it is necessary to connect a local area network to
another local area network or to a wide area network.
Local area network to local area network connections are often
performed with a bridge.
Local area network to wide area network connections are usually
performed with a router.
A third device, the switch, can be used to interconnect segments
of a local area network.
-
8/3/2019 CCN Lecture 6(1)
2/33
2
Why Interconnect?
To separate / connect one corporate division with another.
To connect two LANs with different protocols.To connect a LAN to the Internet.
To break a LAN into segments to relieve traffic congestion.
To provide a security wall between two different types of users.
To connect WLAN to LAN
-
8/3/2019 CCN Lecture 6(1)
3/33
3
Internetworking devices
Descending in increasing power and
complexity
Hubs
Bridges
Switches
Routers
-
8/3/2019 CCN Lecture 6(1)
4/33
4
Hubs
As seen earlier, a hub interconnects two or more workstations
into a local area network. A simple interconnecting device that
requires no overhead to operate.
When a workstation transmits to a hub, the hub immediatelyresends the data frame out all connecting links.
A hub can be managed or unmanaged. A managed hub possesses
enough processing power that it can be managed from a remote
location.
Hubs continue to become smarter.
Some call any interconnection device in a LAN a hub!
-
8/3/2019 CCN Lecture 6(1)
5/33
5
Hubs
Hubs, also called concentrators, expand one Ethernet connection intomany. For example, a four-port hub connects up to four machines (orother network devices) via UTP cables. The hub provides a starconnection for the four ports. Many hubs contain a single BNCconnector as well to connect the hub to existing 10Base-2 networkwiring. The hub also can be connected via one of its ports. One port isdesigned to operate in either Straight-Through or Crossover mode,
selected by a switch on the hub. A hub is similar to a repeater, except it broadcasts data received by any
port to all other ports on the hub. Most hubs contain a small amount ofintelligence as well, examining received packets and checking them forintegrity. If a bad packet arrives or the hub determines that a port isunreliable, it will shut down the line until the error conditiondisappears. Because of its slight delay when processing a packet, thenumber of hubs that may be connected in series is also limited. Severalhubs can be used to connect five Ethernet segments within theaccepted limits. Because each UTP cable may be as long as 100 m, themaximum distance between nodes is 500 m (the network diameter).
-
8/3/2019 CCN Lecture 6(1)
6/33
6
Hubs connecting segments
-
8/3/2019 CCN Lecture 6(1)
7/33
7
Bridges
A bridge can be used to connect two similar LANs, such as two
CSMA/CD LANs.
A bridge can also be used to connect two closely similar LANs,
such as a CSMA/CD LAN and a token ring LAN.
The bridge examines the destination address in a frame and
either forwards this frame onto the next LAN or does not.
The bridge examines the source address in a frame and places
this address in a routing table, to be used for future routing
decisions.
-
8/3/2019 CCN Lecture 6(1)
8/33
8
Bridges vs Routers
Bridge: A bridge is a device that connects two segments of the samenetwork. The two networks being connected can be alike or dissimilar.Unlike routers, bridges areprotocol-independent. They simply forwardpackets without analyzing and re-routing messages.
Router: A router is a device that connects two distinctnetworks. Routers aresimilar to bridges, but provide additional functionality, such as the abilityto filter messages and forward them to different places based on variouscriteria. The Internet uses routers extensively to forward packets fromone host to another.
Based on these definitions we can see that key difference between abridge and router is that a bridge does not look at protocols and a router
does. A bridge does not look at traffic for the purpose of allowing ordisallowing it, and it does not decide what to do with certain types oftraffic; it simply moves data from one network to another. Whereas arouter examines protocols and decides what to do with each packet basedon defined criteria.
-
8/3/2019 CCN Lecture 6(1)
9/33
9
Abridgeinterconnectingtwodissimilar LANs
-
8/3/2019 CCN Lecture 6(1)
10/33
10
Bridgeinterconnectingtwoidentical LANs
-
8/3/2019 CCN Lecture 6(1)
11/33
11
Switches
A switch is a combination of a hub and a bridge.
It can interconnect two or more workstations, but like a bridge, it
observes traffic flow and learns.
When a frame arrives at a switch, the switch examines the
destination address and forwards the frame out the one necessary
connection.
Workstations that connect to a hub are on a sharedsegment.
Workstations that connect to a switch are on a switchedsegment.
-
8/3/2019 CCN Lecture 6(1)
12/33
12
Switches
The backplane of a switch is fast enough to support multiple data
transfers at one time.
A switch that employs a cut-through architecture is one thatpasses on the frame before the entire frame has arrived at the
switch.
Multiple workstations connected to a switch use dedicated
segments. This is a very efficient way to isolate heavy usersfrom the network.
A switch can allow simultaneous access to multiple servers, or
multiple simultaneous connections to a single server.
-
8/3/2019 CCN Lecture 6(1)
13/33
13
Switches vs routers
Switches are considered layer-two devices, using MAC addresses to forwardframes to their proper destination. Routers, layer-three devices, are muchmore complex, using microprocessor-based circuitry to route packets betweennetworks based on their IP address. Routers provide the following services:route discovery; selection of the best route to a destination; adaptation tochanges in the network; translation from one technology to another, such as
Ethernet to token ring; packet filtering based on IP address, protocol, orUDP/TCP port number; and connection to a WAN.
Because of the additional processing required for each packet, a router has ahigher latency than a switch. In addition, a router requires an initial set-upsequence, in which the ports are programmed and certain protocols andcharacteristics are enabled or disabled. A switch may be simply plugged intothe network, automatically learning how to forward frames as the network isused. Note that some protocols (e.g., NetBEUI) cant be routed; instead, theywill pass through a switch. Finally, switches are used within networks toforward local traffic intelligently. Routers are used between networks to routepackets between networks in the most efficient manner.
-
8/3/2019 CCN Lecture 6(1)
14/33
14
Workstationsconnectedtoasharedsegmentofa LAN
-
8/3/2019 CCN Lecture 6(1)
15/33
15
Workstationsconnectedtoadedicatedsegmentofa LAN
-
8/3/2019 CCN Lecture 6(1)
16/33
16
Data Communicationsand ComputerNetworks
Chapter 8
Switches
Major role: isolating traffic patterns and providing multiple
access. This design is usually done by the network manager.
Switches are easy to install and have components that are hot-
swappable.
-
8/3/2019 CCN Lecture 6(1)
17/33
17
A Switch with Two Servers Allowing Simultaneous Access to
Each Server
-
8/3/2019 CCN Lecture 6(1)
18/33
18
Aserverwith twoNICsandtwoconnectionstoaswitch
-
8/3/2019 CCN Lecture 6(1)
19/33
19
Apairofremotebridgesandswitch combination
designedtoisolatenetworktraffic
-
8/3/2019 CCN Lecture 6(1)
20/33
20
Routers (really specialized computers)
The device that connects a LAN to a WAN or a WAN to a WAN
(the INTERNET! uses IP addresses).
A router accepts an outgoing packet, removes any LAN headersand trailers, and encapsulates the necessary WAN headers and
trailers.
Because a router has to make wide area network routing
decisions, the router has to dig down into the network layer ofthe packet to retrieve the network destination address.
-
8/3/2019 CCN Lecture 6(1)
21/33
21
Routers
Thus, routers are often called layer3 devices. They operate at
the third layer, or OSI network layer, of the packet.
Routers often incorporate firewall functions.
An example of a routers operation is shown on the next slide.
-
8/3/2019 CCN Lecture 6(1)
22/33
22
Router conversion of CSMA/CD data frame to an internet
frame as it passes from a LAN to the internet
-
8/3/2019 CCN Lecture 6(1)
23/33
23
Wireless connections: Access Point as a Bridge
-
8/3/2019 CCN Lecture 6(1)
24/33
24
Connections (ingeneral)
Bridges for LANs and hubs.
Switches for LANs and workstations.Routers for LANs and WANs (the Internet).
-
8/3/2019 CCN Lecture 6(1)
25/33
25
Linksys Router for Home Network
-
8/3/2019 CCN Lecture 6(1)
26/33
26
Linksys Router for Home Network
-
8/3/2019 CCN Lecture 6(1)
27/33
27
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
The OSI Reference Model
-
8/3/2019 CCN Lecture 6(1)
28/33
28
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
The Physical Layer Connection
SpecifiesSpecifies
electricalelectricalconnectionconnection
-
8/3/2019 CCN Lecture 6(1)
29/33
29
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
The Physical Layer Connection
Hub
AmplificationAmplificationRegenerationRegeneration
-
8/3/2019 CCN Lecture 6(1)
30/33
30
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
The Data Link Connection
DelineationDelineation
ofof
DataData
ErrorError
DetectionDetection
AddressAddress
FormattingFormatting
-
8/3/2019 CCN Lecture 6(1)
31/33
31
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Bridge
& Switch
The Data Link Connection
-
8/3/2019 CCN Lecture 6(1)
32/33
32
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
The Network Layer Connection
EndtoendEndtoend
routingrouting
-
8/3/2019 CCN Lecture 6(1)
33/33
33
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
Network
Layer
Data Link
Layer
Physical
Layer
Application
Layer
Presentation
Layer
Session
Layer
Transport
Layer
The Network Layer Connection
Router